DATECL50.TXT

                                                            
   Documentation for "The Killer Date Class!" Version 5.00

History                                                    1
Implementation Notes                                       2
Archive Contents                                           2
       DATE50.ZIP                                       2
       DATEAX.ZIP                                       3
Release Notes:                                             3
  v5.0 - JMC -  10/ 1/93                                3
  v4.9 - TML - 01/26/94                                 5
  v4.8 - TML - 11/18/93                                 5
  v4.7 - TML - 09/20/93                                 5
  v4.6 - TML - 08/04/93                                 6
  v4.5 - TML - 06/21/93                                 6
  v4.4 - TML - 06/03/93                                 6
  v4.3 - TML - 3/24/93                                  6
  v4.2 - TML - 3/13/93                                  6
  v4.1 - KAA - 3/7/93                                   8
  v4.0 - CP - 6/27/92                                   8
  v3.1 - ES & CH - 8/5/91                               10
A Word about the Calendar & this Date Class                11
Future possibilities for enhancement, Part I               11
Future possibilities for enhancement, Part II              11
Porting Notes                                              12
Restrictions & Copyrights                                  12

History
In the beginning, Steve Marcus (CIS 72007,1233) posted a
  basic date manipulation/arithmetic class produced with
  Borland C++ 2.0 in the  BPROGB forum, with a request for
  suggestions and enhancements. This was on 6/19/91.

A rather enterprising gentleman by the name of Eric Simon
  (CIS 70540,1522) accepted the challenge, and produced a
  new and improved version in the  course of a project he
  was developing at work. He contributed the results to the
  forum on 6/29/91, also inviting enhancements and
  comments.

About that time yet another enterprising gentleman named
  Christopher Hill developed a need for a universal date
  conversion routine for use in a business project he was
  developing as well.  Browsing the same forum, he
  encountered Eric's class, which provided much of the
  functionality he needed - the basic julian-gregorian and
  day of week conversion algorithms - relieving him of the
  task of researching or re-inventing them. Eric had also
  added overloaded + and - operators for incrementing date
  objects by integer days, as well as several print
  functions.  Chris needed additional features for his
  implementations, thus was born versions 3.0 and 3.1(Hill
  & Simon).

Well, almost a year later I sent out an SOS for a date class
  so I didn't have to re-invent the wheel and lo-and-behold
  Chris responded.  Thus begins the saga of version 4.0!  I
  would like to take this opportunity to do a little
  witnessing: I looked all over for a date class that would
  suit my needs!  I reviewed many implementations from
  strangers and friends alike and I am here to tell ya'
  folks, "It don't 'git no bedder 'n dis!"  This class is
  VERY  cool!  Now I'm not trying to say that there's no
  more room for enhancements (I'd really be crazy then!),
  but I am saying that if your looking for a GOOD date
  class (I'd say commercial quality because I have yet to
  see a commercial product that implemented a date class to
  my satisfaction!) then this is it!  So jump in and add to
  it, make it better and we'll SAVE THE WORLD!  (Ok, so I
  got a little carried away at the end. Just a little...)

No, but really... This is a truly pleasing example of co-
  operation among professionals, and an "object" study in
  the code reusability of OOP, resulting in three releases
  of one class within a single month by three different
  analysts who have never met, and yet another upgrade
  almost a year later by a fourth analyst (myself) and none
  of us have yet to meet!  Chris thanks Steve and Eric for
  their inspiration and generosity, and I thank all three
  as well.

I believe any of us would welcome further comments,
  suggestions and enhancements as well.

Good luck!  May the quest for the perfect date class
  continue!
                      Charles Price
                 *    *    *    *
Well, I must say, this is quite an impressive Date class!!!
  And I must agree with Mr. Kenneth...it's probably one of
  the BEST (if not the best) Date class I've seen so far
  (but then again, I've not seen too many!).

However, I thought it really could take more advantage of
  some of the better features of C++ (ie. encapsulation!).
  Thus, I decided to take on the challenge set forth by the
  aforementioned 'Date'-crazed group.

My changes are listed below in the Version 4.2 section.
  Please let me know of any updates/changes that will
  happen in the future!

And of course, we all welcome any
  comments/suggestions/participations!!!
                Tr¡ Minh Ly  :)
                 *    *    *    *
To continue where Charles & Tr¡ leave off, the class sat
  idle for about 8 months, when suddenly in March of '93,
  three people, still all working independently, decided,
  almost simultaneously, to add their own modifications.
  Kenneth Argo got the ball rolling again, and then Tr¡
  Minh Ly kept it active with regular updates.  During this
  time, I was toiling away, spending about two years, off &
  on, ripping out and replacing it's guts, while try to
  keep up with Tr¡'s updates.
                      James M. Curran
                 *    *    *    *

  v5.0       James M. Curran       72261,355     10/30/94
  v4.9       Clyde Ford            71426,72      
  v4.8       Tr¡ Minh Ly           73062,512     
  v4.7       Tr¡ Minh Ly           73062,512     09/20/93
  v4.6       Tr¡ Minh Ly           73062,512     08/04/93
  v4.5       Tr¡ Minh Ly           73062,512     06/21/93
  v4.4       Tr¡ Minh Ly           73062,512     06/03/93
  v4.3       Tr¡ Minh Ly           73062,512     03/24/93
  v4.2       Tr¡ Minh Ly           73062,512     03/13/93
  v4.1       Kenneth A. Argo       71241,3635    03/07/93
  v4.0       Charles Price         70541,3651    06/27/92
  v3.1       Hill & Simon                        08/05/91
  v3.0       Christopher Hill      72030,2606    07/11/91
  v2.0       Eric Simon            70540,1522    06/29/91
  v1.0       Steve Marcus            72007,1233    06/16/91


Implementation Notes
  All versions prior to 4.0 were written specifically for a
  Borland C++ compiler.  However, version 4.0 was written
  specifically for Microsoft C++ 7.0, and version 5.0
  should work with either of those, and (hopefully) several
  others.  We have attempted to optimize the code by
  including the specification of "const" where applicable,
  the passing of references where advisable, and the use of
  constructor initializers where needed.   However, no
  exhaustive analysis of this subject has been made.

  To get the best overview of the class capabilities run
  the demo program.   It may not look pretty, but with a
  printout of a sample run and the code you should be able
  to get a really good feel for it.   The complete class
  specification is given in the accompanying file, DATE_MAN


Archive Contents

DATE50.ZIP
   The main archive file contains:
DATECL.MAK      make file to compiling class library for MSC
                7.0/ MSVC++
DATEDEMO.MAK    make file to compile & link the demo for MSC
                7.0/ MSVC++
DATECL.PRJ      project file for compiling class library
                under Borland C++ 3.1
DATEDEMO.PRJ    project file for compiling demo under Borland
                C++ 3.1
DATECL50.TXT    This file, in straight ASCII text.
DATE_MAN.TXT    Class reference manual.
DATECL.H        the header file
DATECL.CPP      the member functions
DATEDEMO.CPP    a test program (and a messy one at that!)
DATECL.LIB      a lib file so you can use it even if you don't
              have MSC7.0, or you just don't feel like
              fussin' with it!

DATEAX.ZIP
The Auxillary Package (a separate archive) contains these
  optional files:
DATECL50.DOC    This file, in Word for Windows format.  If
              you have WinWord, use this file instead of
              the ASCII version.  It's formatted properly.
DATE_MAN.DOC    The Class Reference Manual, also in WinWord
              format.
CLSS_DOC.DOT    WinWord template used to create the above
              files.
DATE_MAN.CPP    All the examples given in DATE_MAN.  Should
              just print today's date.  Will assert if
              something goes awry.
BABY.CPP        A simple command-line app that uses the Date
              class. (Written for my Brother, the
              Obstetrician, to calculate due dates.)



Release Notes:
v5.0 - JMC -  10/ 1/93
  Made Class compatible MSC7/VC++ & BC 3.1, using the
  compilers' internal, predefined symbols, thus removing
  the need to manually define _MSC or _BCC.

  Attempted to made compatible with Zortech C++.   I have
  compiled it as best I could using the version of Zortech
  C++ that was provided with Tom Swan's book "Learning C++"
  (c 1991).    This is basically a striped-down rendering
  of version 2.1, with some rather significant limitations,
  notably, a very small maximum file size.  It aborts with
  an "out of memory" error midway through DATECL.CPP,
  DATEDEMO.CPP, and DATE_MAN.CPP.  Only BABY.CPP (in the
  separate auxiliary files archive) compiles completely.
  The others experience no other errors up to the point
  where they run out of memory.  Any field reports from
  people with the full package will be greatly appreciated.
  (see also the Porting Notes section, below)

  Have removed or isolated all MS-DOS specific code.  It
  should now compile (with only slighted reduced
  functionality) with  any C++ based on ANSI C.  (Mainly, I
  get the current date using the ANSI C time()/struct TM
  method, instead of  _dos_getime() ).

  Changed Julian_to_mdy() & mdy_to_julian() to remove
  floating point.  This change, by itself, will reduce the
  EXE size of a program  which uses this class, but
  otherwise doesn't use floating point, by about 15K.
  They're also faster this way.

  Converted data members, that were previously changed from
  ints to chars, back into shorts.  This was a false
  economy.  Since ints are, by definition, the natural data
  size for the hardware, what little we save in data (here,
  2 bytes) space we lose in code space, as the compiler
  generates extra instructions to convert the values into
  ints for processing, then back into chars for storage.
  By my calculation, we'd  have to have a minimum of 30
  date object active at one time just to break even in the
  memory required, plus using chars  adds an (admittedly,
  probably imperceptible) speed lose in processing.

  Removed the graphic line characters from the source code
  files. They looked nice under DOS, but really offended
  Borland's &  Microsoft's Windows IDEs.  (And who knows
  what effect they'd  have an a UNIX terminal?)

  Fixed two bad bugs in the AddMonths() function.  First,
  it assumed that if the date wrapped to the next (or
  previous) year, it would be by only one month.  A more
  subtle bug was that it assumed that it would only wrap by
  one year. eg: Date Indep(7,4,1776);
  Indep.AddMonths(2400); cout << Indep; would output
  "1/4/1777" instead of "7/4/1976" (Really, I DID do this
  before Tr¡ did it in version 4.6; It  just took me a
  while to release this <g>)

  The default year when setting a date from a string is now
  the current year. ie. previously   Date date = "3/15";
  would be "March 15, 0 B.C.E.".  It now uses the current
  year.  Similarly,  when a two-digit year is use, it is
  assumed to  be in this century.  ie, previously  Date
  date = "3/15/93"; would be presumed to be in the first
  century.  It's now assumed to be in 1993.   This can be
  changed with the  setCentury function.   If, for some
  bizarre reason, you  actually want to refer to dates in
  the first century AD, use "setCentury(0);".  This will
  return the class to it's previous behavior.

  The date from string function now just LOOKS at the
  string passed to it, so neither modifies the passed
  string, nor requires a temporary copy of the string.

  Centralized common strings.   This saves some space and
  should make  internationalization rather simple.  I've
  started this by adding  the days, months and  error
  messages for Spanish and German. Compile the class with
  _ESPANOL or _DEUTSCHEN defined. (NOTE:  I'm strictly mono-
  lingual and have gotten this information  from foreign
  language dictionaries.  Any corrections from those who
  actually  speak these languages would be greatly
  appreciated, as would the words for  other languages.
  Also, I've used the standard English letters for the
  foreign word, instead of the "more appropriate" letters
  with accents and umlauts, since there is no standard
  ASCII values for those characters, and I'm trying to make
  this compatible to compilers outside the MSDOS world)

  Numerous minor changes to "tighten" the library up a bit.
  I've made some trivial functions "inline"; in particular,
  the arithmetic and comparison operators.  The only change
  that may break existing code using earlier version of
  this class is that type cast operator has been changed
  from "operator  char *" to "operator const char *" since
  this better reflects the value actually returned.  Even
  under previous versions, attempting to modify the string
  returned would probably not have the desired effect.
  Now, this restriction is merely enforced by the compiler.

  Added "COLLATE" format ("YYYYMMDD") to generate a
  sortable key.  This can be stored in databases and other
  places where it will be accessed by straight C programs,
  or otherwise be unable to use the class comparison
  operators.

  Added enums for the months & days of the week.

  Added a new constructor which creates a date based on a
  certain weekday in a certain week of a month & year.  eg.
  Date(3, MONDAY, MARCH, 1993); builds the Date object for
  the 3rd Monday of March, 1993.  If the first parameter is
  Zero, the last date of that day for the month is used (ie
  Date(0, MONDAY, MARCH, 1993) is the last Monday in
  March).

  Added a new Set() function to go with the above new
  constructor.

  Added functions for a host of holidays.

  Added an output manipulator.  The format style can now be
  changed by using '<<' to "output" one of the format_type
  enums to an ostream, eg cout << Date::EUROPEAN << date1
  << endl;

  Will initialize a simple period (ie Date d4 = ".";) to
  today's date. (I did this because I needed to get a date
  string from the command line)

  Returned the ++ and -- operators to their pre-4.5
  condition.  (They were  correct in the first place.)  In
  case you haven't been paying attention, the saga of the
  auto-incremetors goes as such:  Some time prior to v3.0,
  the prefix incrementers were added to the class.  In
  v4.0, the postfix operators were added, but with
  functionality identical to the prefix operators.  In
  v4.1, the postfix operators were corrected to work in the
  manner expected of postfix operators.  In v4.5, the
  functionality of the prefix & postfix operators was
  reversed, in attempts to fix a nonexistent bug.  They've
  now been restored.  I pointed this out to Tr¡, who
  decided I was taking too long get v5.0 out the door, and
  so fixed them in v4.7.  I've double checked them, and
  given my rabbit's foot a healthy rub, so I really think
  we can put this matter to rest now....

  Wrote proper class description reference manual (in the
  separate document DATE_MAN).  Apologies to Microsoft's
  technical writers who's style for their "Microsoft C/C++
  Class Library Reference" I've rather blatantly stole.  I
  revised much of this file, so that it's a bit better
  organized, and with less redundancy, plus made it clear
  when the word "I" is used, which of the class's seven
  authors is speaking  (or at least "I" tried) . The
  reference manual was created in, and this document
  converted into, Microsoft Word format for editing,  and
  then convert back to simple text for distribution.   The
  Word files are available, and if you have access to MS
  Word, that is the best way to deal with this
  documentation.  A Windows WinHelp version of both these
  documents combined will be forthcoming (eventually, but
  remember, I sat on this library for about a year before
  releasing it, so don't hold your breath).

ú    Since the ANSI/ISO C++ committee working papers
  currently propose a new intrinsic data type, "boolean",
  this has been simulated with an boolean enum, and all member
  functions which formerly return "1 for TRUE, and 0 for
  FALSE",  now return "true" and "false" as defined in this
  enum.   When the standard is complete, and compilers
  recognize these new keywords, this enum can be removed.

v4.9 - TML - 01/26/94

ú    Version 4.9 fixes the Date::AddMonths() member
  function.  The problem was it did not adjust the day value
  after the new month's value have been calculated.  For
  example, if the current date is `08/31/1993' and 6 months is
  added to it using Date::AddMonths(), then the result is:
  02/31/1994.  Date::AddMonths() will now set the day value as
  appropriate for the new month.  If the day value is greater
  than the # of days in that month, then it will roll the
  month over to the next month and set the day value to the
  difference between the day value and the # of days in the
  that month.  Thanks to Patrick Cunningham this bug.
  
ú    This version also expands the Date::isDST()
functionality by adding two new member functions:
Date::setDST() and Date::setSTD().  Date::setDST() sets the
month and day on which DST date begins.  Likewise,
Date::setSTD() sets the month and day on which STD date
begins.  Thanks to Marcelos Cantos for this suggestion.

***********************    WARNING TO BORLAND C++ USERS
  *********************
A  couple  of people have kindly informed me that the  class
Date  is a pre-defined class in Borland C++.  Thus, you will
have  to  rename this class to another name like  xDate,  or
DateCL or whatever is appropriate for your implementation!!!
************************************************************
  *******************
v4.8 - TML - 11/18/93

ú    Version 4.8 adds a new member function Date::isDST()
  which was contributed by Clyde Ford (CIS 71426,72).
  Date::isDST() determines if the current date object is
  "within daylight savings time as defined in the United
  States".  If so, then it will return true, otherwise false
  is returned.

v4.7 - TML - 09/20/93
  Version 4.7 un-fixes the serious bug in the code for
  unary operators ++/--. In other words, they were
  originally correct.  I guess I got really confused when I
  last talked to Jorge.

  Thanks to James M. Curran for informing me of this
  change.  Also, James has a new version of DateClass (5.0)
  currently in the works.  I think all of us will be very
  impress and receptive of his version!!!
v4.6 - TML - 08/04/93
  Fixes the Date::AddMonths() member function.  It does not
  add or subtract the number of months correctly.   Thanks
  to Patrick Cunningham for finding this bug!

v4.5 - TML - 06/21/93
  Fixes a very serious bug in the code for unary operators
  ++/--.  I confused myself with the formats for prefix and
  postfix operations.  (I got them reversed.)  Jorge Padron
  was kind enough to inform me of my mistake.

  I also removed the 'const' keyword from parameter
  statements for functions which require variables to be
  passed by values (as opposed to pass by reference.)  For
  example,
              Date  operator + (const long i);
is changed to:
              Date  operator + (long i);
I did it in the first place because I was trying to be
  consistent, but I realize that this can be confusing
  (especially those that are just learning C++).  Jorge
  also pointed this out to me.

v4.4 - TML - 06/03/93
  Adds a little validation to the value of the day and
  month when an object is created via a string argument.
  For example, month must be from (1..12) and day must be
  from (1..n) where 'n' is the number of days for the given
  month.
Thus, the following statements:
         Date myDate("02/31/1993");
         cout << myDate.formatDate() << "\n";
will result in an "invalid date" output!

v4.3 - TML - 3/24/93
  Add more flexibility in the constructor to support the
  many string formats that are used by the Date class.

  Fixed Date::Date(char *) and made it accept the string as
  a 'const' argument. Also, made a copy of the string
  ('dat') before passing it to strtok() since this function
  modifies its argument!

  Removed the smaller buffer ('buf') and make use of only
  one buffer to save memory.

  Re-coded the type cast operator to call formatDate() so
  the current format and options will be applied to the
  resulting string.

  Changed year to 'int' type to support B.C.E. dates.
v4.2 - TML - 3/13/93

  Made it compatible to both Borland C++ (v 3.1) and
  Microsoft C++ (v 7.0) via #define switches.  Define _BCC
  for Borland and _MSC for Microsoft. See the GO.BAT batch
  file!

  Fix memory problems in Version 4.1.  There were three
  'deadly' memory threats introduced by Version 4.1:

  (a) In the destructor function, it is erroneous to delete
     buf without referring to it as a vector of characters.
     The proper method would be:
              delete [] buf;      // Must have the
     brackets!
  
       Please review the section "The Free Store and Class
       Arrays" on page 95-99 of the _C++ Tutorial_ from
       Microsoft's C++ package!
  
  (b) In the Date::operator char *() function, variable buf
     was allocated space every time the function was called.
     This causes memory leaks when the same Date instance
     calls this operator function more than once during its
     lifetime.
  
  (c) Also in the Date::operator char *() function,
     variable buf was assigned the address of the constant
     string BadDate without prior release of the memory for
     buf.
  
  Fix implementation of the prefix/postfix operators to
  properly reflect the before/after syntax of the unary
  incrementor.  (C++ provides only the facility to
  determine which type of operator is being used, but the
  implementation is left to the programmer!)

  Moved all buffer variables to the class level and made
  them private static member data. for the
  Date::formatDate() function, the buffer is renamed to
  'cbuf' for the Date::Operator () function, the buffer is
  named 'buf'

  Move all publicly declared variables/enums into the
  public portion of the class.  Also redefine the #define
  constants to an enum type.  By doing this, we are taking
  advantage of C++'s encapsulation feature and reduce
  pollution of the global variable names.  This concept is
  based on the ios class. (ie. ios::hex, ios::dec, etc.)

  Also redeclare the 'friend' functions to be member
  functions (again, making use of encapsulation!)

  Rewrote the Date::setOption() function.  (Made it more
  compact!)

  Made use of the 'const' feature of C++ to ensure the
  references returned by most of the member functions will
  be non-modifiable by the calling program. (ie. force them
  to make a copy of it if they want to modify it!)

  In the function Date::formatDate(), for the case
  Date::EUROPEAN and Date::EUROPEAN, fix the code
  (day_of_week < 0) to (day_of_week < 1).  Also removed the
  statement strcat(cbuf, " ") and put the space into the
  sprintf() statement:

  sprintf( cbuf+strlen(cbuf), " %d", abs(year) );
  
  Modified the following functions to return a Date object
  instead of a reference to a Date object!

  Date operator + (const long i);
  Date operator +  (const int  i);
  Date operator - (const long i);
  Date operator - (const int  i);
  Date operator ++ ();
  Date operator ++ (int);
  Date operator -- ();
  Date operator -- (int);
  
  This is important because in Version 4.0 and before, the
     binary operators (+ and -) were declared to return
     references to Date objects since these functions
     dynamically creates a Date object when the function is
     called. However, there were no provisions for deleting
     these objects once they leave the scope of the
     function.
  
  In Version 4.1, Mr. Kenneth got rid of this problem of
     allocation by forcing the compiler to generate code to
     allocate stack space to return the objects.  However,
     Mr. Kenneth 'forget?' to remove the references
     declaration.  Why would this cause problem?  Because
     when the calling program is expecting a reference in
     return (as opposed to a copy of the object), then that
     reference will be invalid since after the function
     terminates, the temporary object (used to return the
     value to the calling program) will also be terminated.
     Thus, the reference to the object is rendered obsolete.

  To test this, I wrote the following program:

  #include "datecls4.h"
  #include "iostream.h"
  
  void showDate(Date &dt)
  {
    cout << dt;    // The (char *) type cast operator is in
  }            // effect here!
  
  void main()
  {
    Date z("04/13/1967");
    showDate(z+3);
  }
  
  RESULT:
    *** destructor called ***          // Temporary object
     is destroyed
    237/7/21
    *** destructor called ***          // Object 'z' is
     destroyed
  

  As dictated by the result, the temporary object (created
     by the + operator) is destroyed before its values are
     displayed.
  
  By declaring the functions to return an actual Date
     object instead of a reference, we force the compiler to
     make a copy of it and return it to the calling program!
v4.1 - KAA - 3/7/93
  Fixed date display when using the * operator to get a
  string pointer.  The code would return xx/xx/  xx if you
  only supplied a 2 digit year.

  Optimized the * operator so Invalid Dates would use a
  common "invalid date" text pointer.

  Fixed the +, - and * operators to get rid cases where
  memory leaks would occur.

  Fixed some variable casts so the code can be compiled
  with /W4

  Added a destructor to delete items created dynamically on
  behalf of the object (ie. char *).

v4.0 - CP - 6/27/92
  Most of the modifications made to version 3.1 were to
  expand the public interface.

  Date &Set() - Sets self to current system date; this may
  also be accomplished by passing initializing a date
  object like so:     Date oDate1("Today");  // See demo
  for examples

  Date &Set(long lJulian) - Sets self to the specified
  julian date

  Date &Set(int nMonth, int nDay, int nYear) - Sets self to
  specified month, day, and year.  The year must be 4
  numbers long, not 2.

  Date &AddWeeks(int nCount = 1) - Add or subtract(use a
  negative int) a specified number of weeks to/from self.

  Date &AddMonths(int nCount = 1) - Add or subtract(use a
  negative int) a specified number of months to/from self.

  Date &AddYears(int nCount = 1); - Add or subtract(use a
  negative int) a specified number of years to/from self.

  int   Day() const - Returns numeric day of the month for
  self

  int   DaysInMonth() - Returns number of days in month
  (1..31)

  int   FirstDOM() const - Returns the First Day Of Month
  for self as a numeric (1..7)

  char *CDOW() - Returns character Day Of Week
  ('Sunday'..'Saturday')

  int   NDOW() const - Returns the numeric day of the week
  for self(1..7)

  int   WOM() - Returns numeric Week Of Month  (1..6)

  int   WOY() - Returns numeric Week Of Year   (1..52)

  char *CMonth() - Character Month name ("January")

  int   NMonth() const - Month Number (1..12)

  Date  BOM() - Returns a new date object that is the First
  Date Of the Month in self.  For example:
  
  Date   Date1;
  Date   Date2("Today");
  Date1 = Date2.BOM();
  
  Date  EOM() - Returns a new date object that is the Last
  Date Of the Month in self.  (See example in BOM() above)

  int   NYear4() const - Returns the numeric value of the
  year for self in the form 1992.

  Date  BOY() - Returns a new date object that is the First
  Date Of the Year in self. (See example BOM() above)

  Date  EOY() - Returns a new date object that is the Last
  Date Of the Year in self. (See example BOM() above)

  Added overloaded operators for + and - to accept int's.

  Added overloaded operators for ++ and -- for Postfix
  notation

  Switched from the Borland style DOS date structure(date)
  to the Microsoft version(_dosdate_t).

v3.1 - ES & CH - 8/5/91
Subsequent to release 3.00, we (Hill & Simon) decided to
  collaborate on several further releases of this date
  class. This, the first, contains two new features, as
  well as a few minor bug fixes.

  There was a minor bug in the original Computer Language
  julian/gregorian date conversion routines having to do
  with negative years.

  The isLeapYear function did not take into account that,
  prior to 1582,   years ending in 00 were also leap years.

  The two-dimensional array of the number of days in each
  month has been eliminated in favor of a computational
  approach.

  The function Date::setFormat(XXXX) maintains a static
  variable (one occurrence for all Date objects, which
  controls the format which the   << operator uses to print
  objects. "XXXX" can be MONTH, MDY, DAY, FULL,   or
  EUROPEAN.  The setting defaults to MDY, but once altered,
  remains altered until reset by another call to setFormat.

  The function Date::setOption(Option, Action) maintains a
  similar static   variable which enables certain print
  formatting options. Available options at this point are: